Recently, the miniaturization and the light weight of a part to be mounted on a mobile communication terminal are required in accordance with the requirement of the miniaturization and the light weight of the mobile communication terminal such as a mobile phone. Moreover, a part including a plurality of functions is also required. In such a situation, a filter and a duplexer which increase an attenuation amount outside a passband are developed. There is a ladder type filter as a filter to be used for the mobile communication terminal.
Patent Documents (Japanese Patent Application Publication Nos. 2010-177770 and 2012-231437) disclose that a plurality of inductors connected to a ground side of a plurality of parallel resonators in a ladder type filter are connected to a common node, and an inductor is connected between the plurality of inductors and a ground.
Since the inductors are provided between the plurality of parallel resonators and the ground, the attenuation amount outside the passband can be increased, but the improvement of the attenuation amount is not sufficient.